Flame detecting apparatus for gas turbine

ABSTRACT

A gas turbine apparatus is provided wherein a turbine is driven or rotated by burning a mixture of a fuel and compressed air and supplying a combustion gas generated by the combustion. A flameout determination unit is provided in the apparatus which is adapted to calculate the air/fuel ratio in the air/fuel mixture, correct the calculated air/fuel ratio to calculate a corrected air/fuel ratio which is substantially constant, compare the calculated corrected air/fuel ratio with a predetermined reference air/fuel ratio, and generate a signal indicative of occurrence of a flameout when the corrected air/fuel ratio is smaller than the reference air/fuel ratio. The corrected air/fuel ratio is calculated by calculating a deviation of a compressor discharge pressure of the compressed air from an air compressor, from a predetermined reference pressure, multiplying the pressure deviation by a predetermined constant, and adding the pressure deviation multiplied by the predetermined constant to the calculated air/fuel ratio. In this way, the corrected air/fuel ratio can be maintained substantially constant even if a load increases in steps.

TECHNICAL FIELD OF THE INVENTION

The present invention relates to a gas turbine apparatus, and moreparticularly, to a gas turbine apparatus which is capable of rapidlydetermining occurrence of a flameout upon starting of the apparatus orduring a load operation thereof.

PRIOR ART

A typical gas turbine apparatus for generating electric power basicallycomprises a turbine rotatably mounted on a rotating shaft; a combustorfor generating a combustion gas; a fuel control valve for adjusting theamount of fuel to the combustor; and an air compressor for sendingcompressed air to the combustor; and a generator. The generator isconnected to the turbine through the rotating shaft, so that theturbine, air compressor and generator are generally configured to beintegrally driven through the rotating shaft.

In such a configuration as described above, a fuel adjusted by the fuelcontrol valve and air compressed by the air compressor (hereinaftercalled the “compressed air”) are supplied to the combustor in which amixture of the compressed air and fuel is formed. Then, the air/fuelmixture is burnt in the combustor to generate a combustion gas which issupplied to the turbine, causing the turbine to revolve at high speeds.As mentioned above, the generator is mounted at one end of the rotatingshaft, so that the generator is driven by the turbine through therotating shaft for generating electric power.

Such a gas turbine apparatus as described above generally comprises acontroller for controlling the turbine which is supplied with thecombustion gas for rotation. The turbine controller conducts a feedbackcontrol for controlling a rotational speed (or the number of rotationper unit time) of the turbine and an acceleration thereof. Specifically,a current speed of the turbine and a current acceleration thereof arefed back to a processor which calculates the amount of supplied fuelwhich minimizes a deviation of the fed-back value from a preset targetvalue. Then, the opening degree of the fuel control valve is operated toprovide the calculated amount of fuel supplied to the combustor, therebyincreasing or decreasing the amount of combustion gas supplied to theturbine to control the number of rotations of the turbine.

Such a foregoing gas turbine apparatus may suffer from so-calledflameout, i.e., sudden extinction of combustion flame while thecombustor is still being supplied with the fuel. This flameout would notonly stop the operation of the gas turbine apparatus but fill the gasturbine apparatus with the supplied fuel or air/fuel mixture which couldignite and explode by residual heat in the turbine or the like, thuscreating an extremely dangerous situation. Therefore, it is critical tobe able to immediately sense a flame-out, if it occurs, to stop thesupply of the fuel.

Possible factors that must be taken into consideration for determiningthe occurrence of a flameout may include a mass flow ratio (or weightflow ratio) of air to fuel in an air/fuel mixture, i.e., an air/fuelratio (A/F). The air/fuel ratio indicates the mass flow ratio of air tofuel, served for combustion, i.e., a mixture ratio, and can becalculated by dividing a flow rate of the air per unit time by a flowrate of the fuel per unit time. As described above, the air iscompressed by the air compressor before it is provided to the combustor,and the air compressor is driven by the turbine, so that the flow rateof the air is proportional to the number of rotations of the turbine.The flow rate of the fuel is proportional to the opening degree of thefuel control valve. Therefore, the air/fuel ratio can be derived fromthe number of rotations of the turbine and the opening degree of thefuel control valve.

Since occurrence of a flameout causes a shut down of the supply ofcombustion gas, the number of rotations of the turbine (the flow rate ofthe air) is suddenly reduced. In response thereto, the opening degree ofthe fuel control valve (and thus the flow rate of the fuel) is increasedby the feedback control for recovering the reduced number of rotations,resulting in a lower air/fuel ratio. Therefore, when an air/fuel ratiowhich is assumed when the flameout occurs, is previously set as areference air/fuel ratio for determining that the flameout has occurred,it is possible to make such a determination when the actual air/fuelratio falls below the reference air/fuel ratio. Based on this strategy,a conventional gas turbine apparatus employs a method which involvesmonitoring a process value of the air/fuel ratio at all times, anddetermines that a flameout has occurred when it senses that the processvalue falls below the set reference air/fuel ratio.

As mentioned above, the gas turbine apparatus comprises the controllerfor controlling the turbine, and conducts a control to maintain aconstant rotational speed with reference to a rotational speed of theturbine in a normal load operation particularly in order to stablyoutput the electric power from the generator. Thus, in the gas turbineapparatus which controls the turbine to maintain a constant rotationalspeed, as the turbine is applied with a load, the amount of suppliedfuel is increased to recover the rotational speed which has once beendecreased due to an increase in the load. In other words, the air/fuelratio becomes smaller in accordance with the magnitude of the load,because an increased amount of fuel is supplied while the turbinecontinues to rotate at the constant rotational speed.

For example, when the magnitude of the load increases in steps, thevalue of the air/fuel ratio becomes smaller in accordance with themagnitude of the load. FIG. 1 shows how respective numerical valueschange in a gas turbine apparatus during such a condition as above. Asshown in FIG. 1, an opening degree FCV of the fuel control valve isincreased in response to a load LOAD which increases in steps, in orderto maintain a rotational speed (or the number of rotations) NR of theturbine constant, with an associated reduction in an air/fuel ratio A/F.In this event, when a reference air/fuel ratio is set, for example, at avalue indicated by A/F(ref1) in FIG. 1, the reduced air/fuel ratio A/Fmay fall below the reference air/fuel ratio (at time t1), resulting inmisidentification of a flameout even though no flameout has actuallyoccurred.

To avoid such misidentification, conventionally, the reference air/fuelratio is set at a value lower than a minimum value of the air/fuelratio, indicated by A/F(ref2) in FIG. 1, which is reduced in response toan increased load to attain a solution.

However, as mentioned above, the reference air/fuel ratio having a lowvalue (A/F(ref2) results in a large difference between the air/fuelratio during a non-load operation (or at rated rotation) and thereference air/fuel ratio, so that it takes a long time before thereduced air/fuel ratio reaches the reference air/fuel ratio.Consequently, there is a large time lag from the occurrence of actualflameout to determination of the occurrence of the flameout. This meansa delay in the timing at which the supplied fuel should be shut down,possibly giving rise to an accident as mentioned above.

It should be noted that even if a load increases substantially in alinear fashion rather than in steps, there is a possibility that theconventional determining method makes misidentification of flameoutoccurrence. When the reference air/fuel ratio is set at a lower value inorder to prevent such misidentification, the aforementioned accident mayarise when the flameout actually occurs.

In addition, since the air/fuel ratio A/F fluctuates depending onoperating conditions in different phases even during a normal operation,the air/fuel ratio may fall below a set reference air/fuel ratio. Such asituation also leads to misidentification of flameout occurrence. Toavoid this misidentification, it is necessary to set the referenceair/fuel ratio, which should be relied on to determine the occurrence ofa flameout, to a value lower than the air/fuel ratio which is expectedto be reduced during a normal operation. Particularly, during a normaloperation, the air/fuel ratio indicates the lowest value upon startingthe gas turbine apparatus.

FIG. 2 is a graph showing how a rotational speed NR of a turbine and anair/fuel ratio A/F fluctuate upon start of a conventional gas turbineapparatus. In FIG. 2, A/F1 indicates the air/fuel ratio during a normaloperation, and A/F(ref) indicates a reference air/fuel ratio. Generally,when the gas turbine apparatus is started up, an air/fuel mixture isignited while the rotation of the turbine is maintained by a startingmotor at a rotational speed at which ignition can be made (from time t1to time t2 in FIG. 2).

As shown in FIG. 2, after time t2 at which the air/fuel mixture isignited, the rotational speed of the turbine accelerates with agradually-increasing amount of fuel supplied thereto. In other words,the air/fuel ratio A/F is increased substantially in proportion to theincreasing rotational speed NR of the turbine. Thus, the air/fuel ratioA/F presents the lowest value immediately after the ignition (at timet2), as shown in FIG. 2. For this reason, conventionally, the referenceair/fuel ratio A/F(ref), which should be relied on to determineoccurrence of a flameout, must be set at a value lower than the air/fuelratio at a time immediately after the ignition, as shown in FIG. 2.

However, the reference air/fuel ratio A/F(ref) set at a low valueresults in an extremely large difference between the air/fuel ratio A/F(=A/F1) and the reference air/fuel ratio A/F(ref) during a normaloperation. Consequently, when a flameout actually occurs, a longer timeis required for the reduced air/fuel ratio to reach the referenceair/fuel ratio, causing a delay of the timing at which the supplied fuelshould be stopped, possibly leading to an accident.

DISCLOSURE OF THE INVENTION

The present invention has been made in view of the problems as mentionedabove, and it is an object of the invention to provide a gas turbineapparatus which is capable of reliably and rapidly detecting occurrenceof a flameout.

In order to attain the object as above, the present invention provides agas turbine apparatus for burning a mixture of a fuel and compressedair, and supplying a turbine with a combustion gas generated by thecombustion to drive the turbine, wherein the gas turbine apparatusincludes a flameout determination unit comprising:

means for calculating an air/fuel ratio in the air/fuel mixture;

means for correcting the calculated air/fuel ratio to calculate acorrected air/fuel ratio which is substantially constant; and

determination means for comparing the calculated corrected air/fuelratio with a predetermined reference air/fuel ratio to generate a signalindicative of occurrence of a flameout when the corrected air/fuel ratiois smaller than the reference air/fuel ratio.

A first embodiment of the corrected air/fuel ratio calculation means ofthe gas turbine apparatus according to the present invention comprises:means for calculating a pressure deviation of a compressor dischargepressure of the compressed air from an air compressor detected bypressure detection means from a predetermined reference pressure, andmultiplying the pressure deviation by a predetermined constant; andmeans for adding the value obtained by multiplying the pressuredeviation and the predetermined constant to the air/fuel ratiocalculated by the air/fuel ratio calculation means to calculate acorrected air/fuel ratio which remains substantially constant even whenthe gas turbine apparatus is applied with an increasing load.

A second embodiment of the corrected air/fuel ratio calculation means ofthe gas turbine apparatus according to the present invention comprises:means for calculating a rotation deviation of a rotational speed of theturbine detected by rotational speed detection means from apredetermined reference rotational speed, and multiplying the rotationalspeed deviation by a predetermined constant; and means for adding thevalue obtained by multiplying the rotational speed deviation and thepredetermined constant to the air/fuel ratio calculated by the air/fuelratio calculation means to calculate a corrected air/fuel ratio whichremains substantially constant during a starting-up condition of the gasturbine apparatus is started.

A third embodiment of the corrected air/fuel ratio calculation means ofthe gas turbine apparatus according to the present invention includesboth of the first and second embodiments of the corrected air/fuel ratiocalculation means. In this case, the determination means comprises afirst determination means for comparing the first corrected air/fuelratio with a first predetermined reference air/fuel ratio to generate asignal indicative of occurrence of a flameout when the first correctedair/fuel ratio is smaller than the first reference air/fuel ratio; and asecond determination means for comparing the second corrected air/fuelratio with a second predetermined reference air/fuel ratio to generate asignal indicative of occurrence of a flameout when the second correctedair/fuel ratio is smaller than the second reference air/fuel ratio.

The present invention is also provided a gas turbine apparatus forburning a mixture of a fuel and air compressed by an air compressor, andsupplying a turbine with a combustion gas generated by the combustion todrive the turbine, wherein the gas turbine apparatus includes a flameoutdetermination unit comprising:

means for calculating an air/fuel ratio in the air/fuel mixture;

means for calculating an acceleration of a rotational speed of theturbine detected by rotational speed detection means;

means for calculating a variation of an exhaust gas temperature of theturbine detected by temperature detection means; and

determination means for determining whether the calculated air/fuelratio is smaller than a predetermined reference air/fuel ratio,determining whether the calculated acceleration of the rotational speedof the turbine is negative, and determining whether the calculatedvariation of the exhaust gas temperature is negative, to generate asignal indicative of occurrence of a flameout when the results of thedeterminations are all affirmative.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a graph for explaining how an increasing load leads tomisidentification of a flameout, even though it has not occurred, in aconventional flameout detecting method in a gas turbine apparatus;

FIG. 2 is a graph for explaining how a flameout is misidentified, eventhough it has not occurred, upon starting the gas turbine apparatus, inthe conventional flameout detecting method in the apparatus;

FIG. 3A is a block diagram illustrating a first embodiment of a gasturbine apparatus according to the present invention; and FIG. 3B is ablock diagram illustrating a configuration of a flameout determinationsection provided in the gas turbine apparatus shown in FIG. 3A.

FIG. 4 is a block diagram illustrating an embodiment of a first flameoutdetermination unit in the flameout determination section illustrated inFIG. 3B;

FIGS. 5 and 6 are graphs for explaining how the first flameoutdetermination unit illustrated in FIG. 4 can avoid erroneous detectionfor flameout even if a load increases in steps and can promptly detect aflameout when it actually occurs;

FIG. 7 is a block diagram illustrating an embodiment of a secondflameout determination unit in the flameout determination sectionillustrated in FIG. 3B;

FIG. 8 is a graph for explaining how the second flameout determinationunit illustrated in FIG. 7 can avoid erroneous detection for flameoutupon starting and can promptly detect a flameout when it actuallyoccurs;

FIG. 9 is a block diagram illustrating a configuration of a gas turbineapparatus in another embodiment according to the present invention;

FIG. 10 is a block diagram illustrating an embodiment of a flameoutdetermination section in the gas turbine apparatus illustrated in FIG.9; and

FIG. 11 is a graph for explaining how the employment of the flameoutdetermination section illustrated in FIG. 10 can prevent erroneousdetection for flameout during a normal operation and can promptly detecta flameout when it actually occurs.

BEST MODE FOR CARRYING OUT THE INVENTION

FIG. 3A is a schematic diagram generally illustrating a configuration ofa gas turbine apparatus according to one embodiment of the presentinvention. As illustrated in FIG. 3A, the gas turbine apparatus 100comprises a turbine 1; a combustor 2 for burning an air/fuel mixture togenerate a combustion gas; a fuel control valve 19 for adjusting theamount of fuel supplied to the combustor 2; and an air compressor 3 forproviding compressed air to the combustor 2. The gas turbine apparatusalso comprises a turbine controller 11 for controlling the turbine 1;and a pressure sensor 20 for detecting a pressure CDP of discharged aircompressed by the air compressor 3.

The turbine 1, which has a plurality of rotor blades for rotation inresponse to a movement of fluid, is rotatably supported within a casing(not shown) through a rotation shaft 6. The air compressor 3 isconfigured to be driven by the turbine 1 through the rotation shaft 6 tocompress air. The air compressor 3 is connected to the combustor 2through a pipe 7, so that air compressed by the air compressor 3 issupplied to the combustor 2 through the pipe 7.

The fuel control valve 19 is disposed upstream of the combustor 2. Afuel supplied from a fuel supply source (not shown) is supplied to thecombustor 2 after it passes through the fuel control valve 19. The fuelcontrol valve 19 has a variable opening, so that the amount of fuelsupplied to the combustor 2 is adjusted by controlling the openingdegree.

The fuel and compressed air supplied to the combustor 2 form an air/fuelmixture in the combustor 2, and the air/fuel mixture is burnt therein togenerate a high-temperature and high-pressure combustion gas. Then, thegenerated combustion gas is supplied to the turbine 1, therebypermitting the turbine 1 to rotate at a high speed.

A rotational speed sensor 12 is disposed near an end of the rotatingshaft 6 for detecting the number of rotations NR of the turbine 1. Thedetected number of rotations NR is communicated to the turbinecontroller 11 which conducts a feedback control for controlling theturbine. A generator 5 is connected to one end of the rotating shaft 6,such that the generator 5 is driven or rotated by the turbine 1 throughthe rotating shaft 6 for generating electric power.

The gas turbine apparatus 100 further comprises an emergency shut-downvalve 4 located between the fuel control valve 19 and a fuel source (notshown), and a flameout determination section 30 for outputting a signalfor closing the emergency shut-down valve 4. As illustrated in FIG. 3B,the flameout determination section 30 is composed of a first flameoutdetermination unit 31 for determining occurrence of a flameout during anormal operation of the gas turbine apparatus 100; a second flameoutdetermination unit 32 for determining occurrence of a flameout uponstarting-up the gas turbine apparatus 100; and an air/fuel ratiocalculation unit 33. The flameout determination section 30 isccommunicated with a signal NR indicative of a rotational speed (or thenumber of rotations per unit time) of the turbine, a signal CDPindicative of a compressor discharge pressure from the pressure sensor20, and a signal FCV indicative of the opening degree of the fuelcontrol valve 19 from the turbine controller 11.

The air/fuel ratio calculation unit 33 calculates the air/fuel ratio A/Fbased on the rotational speed NR and the opening degree FCV of the fuelcontrol valve 19. As mentioned above, air supplied to the combustor 2 iscompressed by the air compressor 3 before it is supplied, and the aircompressor 3 is driven by the turbine 1, so that the flow of the air inan air/fuel mixture is proportional to the rotational speed NR of theturbine 1. The amount of fuel supplied to the combustor 2, in turn, isproportional to the opening degree FCV of the fuel control valve 19.Thus, the air/fuel ratio calculation unit 33 can calculate the air/fuelratio A/F based on the rotational speed NR of the turbine 1 detected bythe rotational speed sensor 12, and the opening degree FCV of the fuelcontrol valve 19 communicated from the turbine control unit 11.

FIG. 4 illustrates a configuration of the first flameout determinationunit 31, i.e., for determining a flameout when the turbine controller 11is controlling the turbine 1 to maintain the rotational speed of theturbine 1 at a rated rotational speed during a load operation. Asillustrated in FIG. 4, the first flameout determination unit 31 iscomposed of a corrected air/fuel ratio calculation unit 311, and acomparison/determination unit 312. The corrected air/fuel ratiocalculation unit 311 adds a predetermined correction value depending onthe discharge pressure CDP of the air compressor 3 to the air/fuel ratioA/F calculated by the air/fuel ratio calculation unit 33 to calculate acorrected air/fuel ratio A/Fc which remains substantially constant. Forthis purpose, the corrected air/fuel ratio calculation unit 311calculates a deviation of the discharge output CDP of the air compressor3 detected by the pressure sensor 20 from a predetermined referencepressure CDP(ref) in a pressure deviation calculation unit 311 a. Thereference pressure CDP(ref) is preferably set to the value of the normalcompressor discharge pressure CDP during an operation at the ratedrotational speed, for example, as shown in FIG. 5. Then, a multiplier311 b multiplies the deviation by a predetermined constant Y tocalculate a correction value ΔCDP·Y, and an adder 311 c adds thecorrection value ΔCDP·Y and the air/fuel ratio A/F calculated by theair/fuel ratio calculation unit 33 to derive a corrected air/fuel ratioA/Fc:A/Fc=ΔCDP·Y+A/FThe constant Y is such a value that makes the corrected air/fuel ratioA/Fc substantially constant, as will be later described.

As illustrated in FIG. 4, the corrected air/fuel ratio A/Fc calculatedin the corrected air/fuel ratio calculation unit 311 is next sent to thecomparison/determination unit 312. The comparison/determination unit 312compares the corrected air/fuel ratio A/Fc received from the correctedair/fuel ratio calculation unit 311 with a previously set referenceair/fuel ratio A/F(ref), and outputs a signal indicating that a flameoutoccurs when the former is lower than the latter. Then, the emergencyshut-down valve 4 disposed upstream of the combustor 2 is closed inresponse to this signal to immediately shut down the supply of fuel tothe combustor 2.

The reason that the corrected air/fuel ratio A/Fc calculated asdescribed above remains substantially at a constant value, will beexplained with reference to FIGS. 5 and 6. In the gas turbine apparatuswhich controls the turbine 1 to make the rotational speed NR constant,when a load LOAD applied to the turbine 1 is increased in steps, theamount of supplied fuel (proportional to FCV) is increased by a feedbackcontrol for recovering the rotational speed NR of the turbine 1 whichtends to decrease (see FIG. 1).

In response, the air/fuel ratio A/F is reduced in proportion to themagnitude of the load, as shown in FIG. 5. Also, since the amount ofturbine work is simultaneously increased with the increase in the amountof supplied fuel, due to the increased volume flow rate of hightemperature combustion gas, the discharge pressure CDP of the compressedair is also increased substantially in proportion to the magnitude ofthe load. In other words, the air/fuel ratio A/F behaves substantiallyin reciprocal proportion to the discharge pressure CDP of the compressedair, as shown in FIG. 5. It is, therefore, possible to find thecorrection value ΔCDP·Y which compensates the reduction of the air/fuelratio A/F by appropriately setting the predetermined constant Y shown inFIG. 4. Then, by adding the correction value ΔCDP·Y to the actual orcalculated air/fuel ratio A/F, the corrected air/fuel ratio A/Fccalculated by the corrected air/fuel ratio calculation unit 311 can bemade substantially constant. For reference, Y is an empirically derivedvalue obtained through a test using the actual apparatus, such thatΔCDP·Y+A/F is made substantially constant.

Since the corrected air/fuel ratio A/Fc is reduced when a flameoutactually occurs, this corrected air/fuel ratio can be used as a factorfor determining the occurrence of the flameout. As shown in FIG. 6, thereference air/fuel ratio A/F(ref) is set at a value slightly smallerthan the corrected air/fuel ratio A/Fc during a non-load operation, andoccurrence of a flameout is determined when the corrected air/fuel ratioA/Fc falls below the reference air/fuel ratio A/F(ref).

With the employment of the determining method as described above, thecorrected air/fuel ratio A/Fc remains substantially constant even when aload fluctuates during a nomal operation, so that no determination ismade that a flameout occurs. Then, since the corrected air/fuel ratioA/Fc is reduced only when a flameout actually occurs, the occurrence ofthe flameout can be precisely determined. Moreover, the referenceair/fuel ratio A/F(ref) can be set to a value closer to the correctedair/fuel ratio A/Fc during a non-load operation, as compared with theconventional set value A/F(ref1), as shown in FIG. 6. Therefore, as thecorrected air/fuel ratio is reduced in response to a flameout, itreaches the reference air/fuel ratio A/F(ref) soon, and as a result, itis possible to extremely rapidly determine the flameout occurrence.

As described above, according to the first flameout determination unit31 described above, in the gas turbine apparatus which controls theturbine such that the rotational speed remains constant, even when thegas turbine apparatus is subjected to an increasing load condition, theaforementioned correction value is added to the air/fuel ratio to derivethe corrected air/fuel ratio which is a substantially constant value.Thus, this corrected air/fuel ratio is monitored, so that the referenceair/fuel ratio, which is relied on to determine occurrence of aflameout, can be set to a value approximate to the corrected air/fuelratio. As a result, since the corrected air/fuel ratio, which is reducedupon occurrence of an actual flameout, reaches the reference air/fuelratio quickly, it is possible to extremely rapidly sense that theflameout has occurred.

FIG. 7 illustrates a configuration of the second flameout determinationunit 32, i.e., for precisely determining a flameout upon starting-up thegas turbine apparatus 100. FIG. 8 is a graph showing changes in therotational speed NR of the turbine, and the air/fuel ratio A/F uponstart of the gas turbine apparatus.

As illustrated in FIG. 7, the second flameout determination unit 32 iscomposed of a corrected air/fuel ratio calculation unit 321, and acomparison/determination unit 322. In the corrected air/fuel ratiocalculation unit 321, a rotation deviation calculation unit 321 acalculates a deviation ΔNR of the rotational speed NR of the turbine 1detected by the rotational speed sensor 12 from a predeterminedreference rotational speed NR(ref), and a multiplier 321 b multipliesthe deviation ΔNR by a predetermined constant Z to calculate acorrection value ΔNR·Z. Then, an adder 321 c adds the corrected valueΔNR·Z and the air/fuel ratio A/F calculated by the air/fuel ratiocalculation unit 33 to derive a corrected air/fuel ratio A/Fc′:A/Fc′=A/F+ΔNR·Z

The corrected air/fuel ratio A/Fc′ thus calculated is found as asubstantially constant value. The reason for this fact will be explainedwith reference to FIG. 8. Upon starting-up the gas turbine apparatus100, the rotational speed NR of the turbine 1 after the ignition (attime t2) increases at a substantially constant acceleration, as shown inFIG. 8, because of the increment of the amount of fuel. In other words,the rotational speed NR of the turbine 1 behaves substantially inproportion to the air/fuel ratio A/F. Therefore, by appropriatelysetting the reference rotational speed NR(ref), the deviation ΔNR of therotational speed NR of the turbine 1 from the reference rotational speedNR(ref) presents a value which fluctuates substantially in proportion tothe value of the air/fuel ratio A/F. It should be noted that a ratedrotational speed during a non-load operation is preferably employed forthe reference rotational speed NR(ref). Further, the constant Z can befound such that the correction value ΔNR·Z obtained by multiplying thedeviation and constant Z compensates the reduction of the air/fuel ratioA/F. Consequently, the corrected air/fuel ratio A/Fc′ calculated by thecorrected air/fuel ratio calculation unite 321 can be maintainedsubstantially constant by adding the correction value ΔNR·Z to theair/fuel ratio A/F.

Next, the corrected air/fuel ratio A/Fc′ calculated as described aboveis sent to the comparison/determination unit 322. Thecomparison/determination unit 322 determines, based on the correctedair/fuel ratio A/Fc′ sent from the corrected air/fuel ratio calculationunit 321, whether or not a flameout occurs. Specifically, apredetermined reference air/fuel ratio A/F′(ref) has been set at thecomparison/determination unit 322, such that thecomparison/determination unit 322 generates a signal indicating that aflameout has occurred when the corrected air/fuel ratio A/Fc′ fallsbelow the reference air/fuel ratio A/F′(ref). As this signal isgenerated, the emergency shut-down valve 4 is operated to shut down thesupply of fuel to the combustor 2.

As described above, the corrected air/fuel ratio A/Fc′ calculated by thecorrected air/fuel ratio calculation unit 321 is substantially constanteven upon starting up the gas turbine apparatus 100. Therefore, thereference air/fuel ratio A/F′(ref) can be increased to and set at avalue closer to the corrected air/fuel ratio A/Fc′, as shown in FIG. 8,as compared with that (A/F(ref1)) which is set in the conventionalflameout detecting method. As a result, when a flameout actually occurs,the corrected air/fuel ratio A/Fc′ is immediately reduced to thereference air/fuel ratio A/F′(ref), thereby making it possible toextremely rapidly determine that the flameout has occurred. In this way,any accident possibly caused by the occurrence of the flameout can beobviated.

In the first and second flameout determination units 31 and 32, whenA/F(ref) can be set equal to A/F′(ref) through a test using an actualapparatus, the comparison/determination units 312, 322 may be integratedinto one which can be used in common.

FIG. 9 illustrates a gas turbine apparatus 100′ which comprises aflameout determination unit 30′ in another embodiment according to thepresent invention. The flameout determination unit 30′ determineswhether or not a flameout occurs during a normal operation of the gasturbine apparatus. The gas turbine apparatus 100′ comprises atemperature sensor 17 which is installed in a pipe on the gas exhaustside of the turbine 1 for detecting a temperature of exhaust gases(mainly, a combustion gas). A signal EGT indicative of the exhaust gastemperature detected by the sensor 17 is communicated to the flameoutdetection unit 30′ together with a signal NR indicative of therotational speed from a rotational speed sensor 12, and a signal FCVindicative of the opening degree of the fuel control valve 19 from aturbine controller 11. As illustrated in FIG. 10, the flameoutdetermination unit 30′ comprises an air/fuel ratio calculation unit 33for calculating an air/fuel ratio of air to fuel in the mixture, atemperature variation calculation unit 34 for calculating a variation ofthe exhaust gas temperature EGT from the temperature sensor 17; anacceleration calculation unit 35 for calculating an acceleration speedACCEL of the turbine 1 based on the rotational speed NR detected by therotational speed sensor 12; and a comparison/determination unit 36 fordetermining occurrence of a flameout.

As mentioned above, the air/fuel ratio calculation unit 33 calculatesthe air/fuel ratio based on the rotational speed of the turbine 1 fromthe rotational speed sensor 12, and the opening degree of the fuelcontrol valve 19 from the turbine control unit 11.

The temperature variation calculation unit 34 samples the temperatureEGT measured by the exhaust temperature sensor 17 at predeterminedintervals, and compares each sampling value with the preceding samplingvalue to calculate the variation ΔEGT of the exhaust gas temperature.

The comparison/determination unit 36 is communicated with the valuescalculated by the air/fuel ratio calculation unit 33, temperaturevariation calculation unit 34 and acceleration calculation unit 35,respectively. Then, the comparison/determination unit 36 determineswhether or not a flameout has occurred based on these calculated values.Specifically, the comparison/determination unit 36 outputs a signalindicating that a flameout has occurred only in such a case that theair/fuel ratio A/F calculated by the air/fuel ratio calculating unit 33is below a predetermined reference air/fuel ratio A/F(ref), thetemperature variation ΔEGT for the exhaust gas temperature calculated bythe temperature variation calculation unit 34 is negative, and therotational speed acceleration ACCEL of the turbine 1 calculated by theacceleration calculation unit 35 is negative. Then, the emergencyshut-down valve 4 is operated to immediately shut down the supply offuel to the combustor 2.

The reason that the air/fuel ratio A/F, exhaust gas temperature EGT andthe acceleration ACCEL of the turbine 1 can be employed as factors fordetermining occurrence of a flameout, will be explained with referenceto FIG. 11. FIG. 11 is a graph showing fluctuations over time of theair/fuel ratio A/F, exhaust gas temperature EGT, rotation speed NR, andacceleration ACCEL, and the opening degree FCV of the fuel controlvalve, when a flameout occurs in the gas turbine apparatus 100′. As theflameout occurs at time t1, combustion flame extinguishes so that theturbine 1 is not supplied with the combustion gas, resulting in adecrease in the rotational speed NR of the turbine 1, as shown in FIG.11. In response thereto, the opening degree FCV of the fuel controlvalve is increased by a feedback control for increasing the decreasingrotational speed NR, and as a result, the air/fuel ratio A/F changes ina decreasing direction. Also, since the combustion flame extinguishes,the temperature of the combustion gas, i.e., the exhaust gas temperatureEGT also decreases. Since the rotational speed NR of the turbine 1 isdecreased, the acceleration ACCEL of the turbine 1 turns into a negativevalue.

In this way, phenomena which appear when the flameout occurs, include areduction in the air/fuel ratio A/F, a reduction in the exhaust gastemperature EGT, and a negative acceleration ACCEL of the turbine 1. Itis therefore possible to precisely determine the occurrence of aflameout by monitoring these phenomena at all times or continuously, anddetermining that the flameout has occurred only when the air/fuel ratioA/F falls below the previously set predetermined reference air/fuelratio A/F(ref), the variation of the exhaust gas temperature EGT turnsinto negative, and the rotation acceleration ACCEL of the turbine 1turns into negative.

With the employment of the flameout determining method as describedabove, the exhaust gas temperature EGT does not decrease when the gasturbine apparatus 100′ is subjected to an increasing load condition,thereby preventing incorrect determination that a flameout has occurred.Also, since the occurrence of a flameout is determined only when theaforementioned three criteria are satisfied, it is possible to preventmisidentification of a flameout when a load applied to the gas turbineapparatus 100′ is increased to cause a reduction in the air/fuel ratio.Further, in a case that only the air/fuel ratio is simply employed as afactor for determining the occurrence of a flameout as in a prior art,the reference air/fuel ratio must be set relatively low as indicated byA/F(ref1) in FIG. 11. In contrast, the flameout determining method ofthe present invention can set the reference air/fuel ratio A/F(ref)higher than that in the prior art. As a result, when a flameout actuallyoccurs, the reduced air/fuel ratio A/F promptly reaches the referenceair/fuel ratio A/F(ref), permitting a rapid determination of theoccurrence of the flameout. It is therefore possible to stop supplyingthe fuel immediately after the flameout actually occurs, therebyobviating an accident.

The second flameout determination unit 32 illustrated in FIG. 7 may beincorporated into the flameout determination unit 30′ described withreference to FIGS. 9 to 11. In this way, misidentification of a flameoutcan be prevented not only during a normal operation of the gas turbineapparatus 100′ but also upon starting. It should be understood that thegas turbine apparatus according to the present invention is not limitedto the foregoing embodiments, but a variety of modifications can be madewithout departing from the spirit and scope of the present invention.

1. A gas turbine apparatus for burning a mixture of a fuel and compressed air, and supplying a turbine with a combustion gas generated by the combustion to drive the turbine, wherein the gas turbine apparatus includes a flameout determination unit comprising: means for calculating an air/fuel ratio in the air/fuel mixture; means for correcting the calculated air/fuel ratio to calculate a corrected air/fuel ratio which is substantially constant during an absence of a flameout; and determination means for comparing the calculated corrected air/fuel ratio with a predetermined reference air/fuel ratio to generate a signal indicative of occurrence of a flameout when the corrected air/fuel ratio is smaller than the reference air/fuel ratio.
 2. A gas turbine apparatus according to claim 1, wherein the corrected air/fuel ratio calculation means comprises: means for calculating a pressure deviation of compressed air from an air compressor detected by pressure detection means from a predetermined reference pressure, and multiplying the pressure deviation by a predetermined constant; and means for adding the value obtained by multiplying the pressure deviation and the predetermined constant to the air/fuel ratio calculated by the air/fuel ratio calculation means to calculate a corrected air/fuel ratio which remains substantially constant even when the gas turbine apparatus is applied with an increasing load.
 3. A gas turbine apparatus according to claim 1, wherein the corrected air/fuel ratio calculation means comprises: means for calculating a rotation deviation of a rotational speed of the turbine detected by rotational speed detection means from a predetermined reference rotational speed, and multiplying the rotational speed deviation by a predetermined constant; and means for adding the value obtained by multiplying the rotational speed deviation and the predetermined constant to the air/fuel ratio calculated by the air/fuel ratio calculation means to calculate a corrected air/fuel ratio which remains substantially constant during a starting-up condition of the gas turbine apparatus is started.
 4. A gas turbine apparatus according to claim 1, wherein the corrected air/fuel ratio calculation means comprises first and second corrected air/fuel ratio calculation means, and wherein the first corrected air/fuel ratio calculation means comprises: means for calculating a pressure deviation of compressed air from an air compressor detected by pressure detection means from a predetermined reference pressure, and multiplying the pressure deviation by a predetermined constant; and means for adding the value obtained by multiplying the pressure deviation and the predetermined constant to the air/fuel ratio calculated by the air/fuel ratio calculation means to calculate a first corrected air/fuel ratio which remains substantially constant even when the gas turbine apparatus is applied with an increasing load, and the second corrected air/fuel ratio calculation means comprises: means for calculating a deviation of the rotational speed of the turbine detected by rotational speed detection means from a predetermined reference rotational speed, and multiplying the rotational speed deviation by a predetermined constant; and means for adding the value obtained by multiplying the rotational speed deviation and the predetermined constant to the air/fuel ratio calculated by the air/fuel ratio calculation means to calculate a second corrected air/fuel ratio which remains substantially constant during a starting-up condition of the gas turbine apparatus is started.
 5. A gas turbine apparatus according to claim 4, wherein the determination means comprises a first and second determination means, wherein: the first determination means is adapted to compare the first corrected air/fuel ratio with a first predetermined reference air/fuel ratio to generate a signal indicative of occurrence of a flameout when the first corrected air/fuel ratio is smaller than the first reference air/fuel ratio; and the second determination means is adapted to compare the second corrected air/fuel ratio with a second predetermined reference air/fuel ratio to generate a signal indicative of occurrence of a flameout when the second corrected air/fuel ratio is smaller than the second reference air/fuel ratio.
 6. A gas turbine apparatus according to claim 1, wherein the correcting means is adapted to calculate the corrected air/fuel ratio on the basis of an exhaust gas temperature or a rotational speed of the turbine.
 7. A gas turbine apparatus for burning a mixture of a fuel and air compressed by an air compressor, and supplying a turbine with a combustion gas generated by the combustion to drive the turbine, wherein the gas turbine apparatus includes a flameout determination unit comprising: means for calculating an air/fuel ratio in the air/fuel mixture; means for calculating an acceleration of a rotational speed of the turbine detected by rotational speed detection means; means for calculating a variation of an exhaust gas temperature of the turbine detected by temperature detection means; and determination means for determining whether the calculated air/fuel ratio is smaller than a predetermined reference air/fuel ratio, determining whether the calculated acceleration of the rotational speed of the turbine is negative, and determining whether the calculated variation of the exhaust gas temperature is negative, to generate a signal indicative of occurrence of a flameout when the results of the determinations are all affirmative. 